Carbon dioxide indicator



FIG. 1 is a side view of a carbon dioxide indicator showing my new design;

FIG. 2 is a top view thereof;

FIG. 3 is a bottom view thereof;

FIG. 4 is a left end view thereof;

FIG. 5 is a right end view thereof;

FIG. 6 is a top perspective view thereof; and,

FIG. 7 is a bottom perspective view thereof. 

The ornamental design for the carbon dioxide indicator, as shown and described. 